I’ve read a very interesting article in one of the recents IEEE Software magazines by Darja Smite, Fabio Calefaro and Claes Wohlin: http://www.computer.org/cms/Computer.org/ComputingNow/issues/2015/08/mso2015040026.pdf
The authors look critically at the body of knowledge in the area trying to find evidence of the cost savings. The results are that the evidence is not in the published articles. Does that mean that it is not possible to publish about it? or does it mean that there is no real evidence and the companies make decisions based on the “gut-feeling”?
It will be interesting to observe what happens with the body-of-knowledge on the topics in the longer run.